Suppose a random sample of 10 firms gave a mean profit of $900,000 and a (sample) standard deviation of $100,000. Establish a 95% confidence interval for the true mean profit in the industry. Which probability distribution do you use? Why?

Suppose a random sample of 10 firms gave a mean profit of $900,000 and a (sample) standard deviation of $100,000. Establish a 95% confidence interval for the true mean profit in the industry. Which probability distribution do you use? Why?

Use the t-distribution because the population sd is unknown. Although n is small (n < 30), from your previous question it's known that the data comes from a normal population so using the t-distribution is OK.